The present invention relates to an ergometer apparatus, such as an ergometer bicycle or an ergometer rowing apparatus, comprising a flywheel, means actuated by muscle power for driving the flywheel, and a brake device for the flywheel comprising a stationary brake string frictionally engaging a peripheral surface rotating with the flywheel.
In addition to a training of the person using an ergometer apparatus, such apparatus is used to obtain an accurate measurement of the work performed. The work is proportional to the number of revolutions of the flywheel and the frictional force braking the flywheel. The number of revolutions of the flywheel is easily measured, whereas the frictional force is difficult to measure and is above all difficult to maintain constant in operation of the apparatus. In ergometer bicycles there is often used a nylon string which encircles the flywheel and which is tightened in order to obtain the desired frictional force. The frictional force depends on the coefficient of friction and the tightening force, both of which vary with the temperature and are therefore influenced by the generated frictional heat. A certain frictional force set before the apparatus is put into operation will therefore usually change during operation.
According to a previous suggestion (which is believed not to be published prior to the priority date of the present invention) the end of the string which would be the rear end if the string had moved with the rotating peripheral surface, may be loaded by a certain force S, and the string may be wound so many times around the peripheral surface that the necessary load s in the opposite end of the string may be disregarded, whereby the frictional force F may be assumed to be approximately equal to S. However, experience shows that it is not possible to reduce the load s on the forward end of the string to such a negligible value, since a variation in the coefficient of friction may cause the rotating peripheral surface to carry with it the brake string. In practical embodiments the force s has therefore been of the magnitude of 7 to 8 per cent of S, which is much too large for this force to be ignored if a satisfactory accuracy is to be achieved. It has also been suggested that the error in the work measurement introduced by the ignorance of s may correspond to the frictional losses in the transmission, but this is a presumption which is much too rough to be satisfactory in accurate work measurements.